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I walked someone through a super secret strategy of mine, one which I have not shown anyone yet. I did that on purpose because I wanted him to have as little competition as possible with bigger trading post players. The mistakes he made taught me a few things about the way I teach players to flip items. In this case it was a specific level range and quality of armor that few flip (I know because the buy orders are non existent besides mine but they sell reliably every time).
For armor (and weapons), you can't just throw a 250 buy order up without any idea of what you're doing. While this is what I do once I really know my market (and I cancel it to create a new one if too many buy orders overcut me) it is not what I recommend that new players do.
When I told this person to try this new market, which consisted of around two dozen items, he picked one and placed 36 buy orders on that piece of armor. This is NOT what you want to do (btw I am not making fun of the person I was helping, they needed help and I think you can learn from their mistakes). Instead, put 3-5 by orders on every item in the entire category, assuming that every one is still profitable.
Profit = (.85 * sell price) - buy order.
For those that are flipping in the smaller profit range, don't forget to subtract 1 copper from the sell price and add one copper to the buy order if it's going to be close. You are going to overcut and undercut in most cases, so you better factor that in to the equation!
It costs nothing to cancel a buy order, so come back in an hour and cancel any that didn't get fulfilled. Recreate your buy orders for every item, and then go to selling. When you sell, don't list everything at once. List 1-2 of each item.
Be realistic about how much you're going to make from this method. It takes a good bit of time, but I literally am able to double my investment. When you get good at it, you'll play less markets but with much larger buy orders. I currently put out 5 sets of 250 buy orders where the items cost me 2-3 silver each. I then turn around and sell those items in large stacks for 6-10 silver each. I'm talking per item, so that's a profit of around 6 gold 87 silver 50 copper for those 5 markets. I cancel buy order AND sell listings where necessary because I know I can take the profit hit if people get too competitive with my orders.
You also need a very large amount of bag space while doing this, as it takes time to grab all the items and relist them (they don't stack).
For a novice player who just wants some starter cash, this works great. Especially in the 5 silver to 10 silver profit range. When you get crazy good at it, you can go down to the items that sell for 60-100 copper but only cost 10-20 copper to acquire. Making 5x your investment is killer but you also need to give up the time it takes to play at that level. I'm still testing it out before revealing on the private forums and potentially the blog.